Orthopantomography, Scannography, Linear Tomography and Cephalography are complementary radiographic techniques, often combined in a single equipment, of widespread use in dental radiology to obtain respectively a comprehensive survey of the maxillo-facial complex, tomographic views of selected anatomical districts under transversal or axial projections, and cranial views under multiple projections, supporting the diagnosis in the dental prevention, restoration and follow up.
Orthopantomography aims to produce a radiographic image of a curved plane approximating the patient jaws, with blurring of the anatomical structures laying outside a narrow layer around the predesignated curved plane, by using the relative movement of the radiographic film versus the rotation of the x-ray source to generate the layer forming effect.
Scannography has a layer forming process similar to Orthopantomography, where the object is typically laying on a flat plane. It is practically used to produce axial or transverse views of specific anatomical districts, such as the jaw, the joints and the sinus.
Linear Tomography is an alternative technique, using the classic linear tomographic layer forming projection. It is practically used to produce axial or transverse views of specific anatomical districts in the jaw.
Cephalography is a stationary radiographic technique, aiming to produce radiographic images of the cranial complex under various projections, with minimum magnification and geometrical distortion.
For all the indicated radiographic modalities the real-time digital x-ray image acquisition is nowadays a more and more demanded feature. It provides instant image acquisition with reduced x-ray dosage, by taking advantage of the improved performances and reduced costs provided by the modern image imager technology. It also allows safer and cleaner operation, by removal of the film processing and related chemicals.
Both in conventional and digital modality, performing the radiographic techniques above typically requires a mechanical structure capable of performing orbital movements around the patient with simultaneous translation of the rotational centre.
A first difference is that in conventional Panoramic Radiography and Scannography the x-ray film is simultaneously translated at a speed such to obtain the blurring of the anatomical structures laying outside of the plane of interest, while in real time digital applications the x-ray film is replaced by the x-ray imager and special electronic techniques are used to produce the same blurring effect.
A second difference is that in conventional Cephalography and Linear Tomography a stationary x-ray film is used, while in real-time digital applications the stationary x-ray film can be replaced by a stationary x-ray imager.
Alternatively, to significantly reduce the system cost, a linearly shaped x-ray imager will be preferably used, and the image acquisition will be performed by using a horizontal or vertical scanning technique.
Another important difference is that, due to the high cost of the x-ray imager, in real-time digital applications it will be very desirable to have an apparatus and method to relocate the x-ray imager, either manually or automatically, from the Panoramic to the Cephalographic position.
The fundamental concept on which this invention is based was described in prior art application (U.S. Pat. No. 4,985,907), where the roto-translatory system is disclosed realized by two independent translations movements in a plane and one independent rotation movement about an axis perpendicular to that plane. The present invention further expands this concept, by disclosing the new apparatuses and methods required for the real-time digital implementation of the indicated radiographic modalities.
Other prior art (U.S. Pat. No. 4,741,007) describes apparatus and methods in which the roto-translatory movement is realised by means of two pivot shafts placed at a constant distance from each other, using a guide groove and an active actuator.
Further prior art (U.S. Pat. No. 5,012,501) describes apparatus and methods in which a variety of orbital movements is produced by using a first drive for the rotational movement, a second drive for the linear translation of the rotation centre, and a selector for selecting the direction of the linear motion.
More recent prior art (WO 99/17659) describes apparatus and methods in which pivot shafts connecting multiple body parts are driven by active actuators in a SCARA arrangement, allowing a variety of projection movements as required for various dental x-ray imaging modalities.
The concept of the three independent roto-translatory movements disclosed in prior art (U.S. Pat. No. 4,985,907) has proven its flexibility in producing multiple orbital projections by simple adjustment of the software programming data, and can be advantageously used for the generation of the orbital movements required for Orthopantomography, Scannography, and Linear Tomography, both in Conventional and Real-Time Digital Radiography.
The main difference will be that in Real-Time Digital Radiography the film cassette with its independent drive is removed, and is replaced by the x-ray imager having an active area of a size equivalent to the x-ray field at the film plane as used in Conventional Radiography.
However, it will be the purpose of this invention to further exploit the basic concept in order to implement the following desirable features:                Perform Real-Time Digital Cephalography by means of horizontal, vertical or rotatory scanning movements, allowing at the same time ergonomic and reproducible immobilisation of the patient by suitable positioning system.        Perform automatic relocation of the x-ray imager between the Panoramic and Cephalographic positions, in order to allow use of the same imager in both imaging modalities.        